@Yang56 hello...first of all you should factory reset your router and freshly setup the router. After that check it resolved or not...I am curious to know what other devices get disconnected...

If all smartphone and computer gets disconnected, after even factory reset...

Then there is surely and interference problem...

Make sure to put router on a height of 6 feet or more, in the central part of your home, without anything covering the router surrounding...do not put the router near wall or matalic surface...router should be sitting horizontally with antenna vertical as per optimal reception...

Next thing you should do is download a wifi analyzer app, and check the channels of neighbour wifi networks, and set channel manually and also the channel width...

Hoping that should definitely solve your problem....please respond if anything works..

@Namann1 Hello and thank you for your answer !

My second home is in a very isolated area, there is no neighboring WiFi network around. By the way, I don't have access to the wired network, that's why I use a 4G router. The box is placed in the middle of a room, at a satisfactory height.

I have three electric heaters from three different brands connected to this 4G router. Today, two of these radiators are disconnected, I can no longer interact with them remotely. The last radiator is connected. Next time I go there I will do a factory reset (maybe next week). Hope this solves the problem...